Constrained diffusional creep in UHV-produced copper thin films |
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Affiliation: | 1. National Physical Laboratory (CSIR), K.S. Krishnan Road, New Delhi 110 012, India;2. Department of Physics, Indian Institute of Technology Delhi, New Delhi 110 016, India;3. Advanced Technology Institute, University of Surrey, Guildford, GU2 7XH Surrey, United Kingdom;4. Department of Electronic Engineering, University of Surrey, Guildford GU2 7XH, Surrey, United Kingdom |
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Abstract: | The thermomechanical behavior of metallic thin films on stiff substrates is relevant for thin-film devices, but its mechanisms are not fully understood. In this investigation, the mechanical properties of pure Cu and Cu–1 at.% Al films on diffusion-barrier coated Si substrates were studied with the wafer-curvature technique. In ultra-pure films, which were sputtered and annealed under ultra-high vacuum conditions, characteristic stress relaxation at high temperatures was measured, which could be clearly attributed to diffusional creep. Good quantitative agreement with a recent model of diffusional creep constrained by a substrate was obtained. These features were absent in the Cu–Al alloy films, in which Al surface segregation and oxidation had produced a “self-passivating” effect, and in films produced in less clean environments. Based on these results, we propose a model of thin-film deformation based on dislocation glide and constrained diffusional creep. |
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